The field of the invention is that of deployable structures that can advantageously be used in deployable telescopes or in any other space of other system.
Currently, the increasing demands for high resolution, both for observation of the Earth from space and for deep space observation (detecting objects that are very weakly lit while maintaining the exposure time within the limits imposed by the stabilisation capability), necessitate increasingly large space observation systems.
Moreover, missions of observation of the Earth from a geostationary orbit can be envisaged with the associated gains (greater thermal stability, fewer disturbances due to gravity, permanent observation above an area) but, given the distance, require greater aperture areas.
To successfully complete these missions, very large telescopes have to be designed and, in most cases, their dimensions exceed the available volume in the nosecone of the launch vehicle.
The design of such systems brings with it many technological challenges such as the development of deployable structures of large dimensions and active systems that can be used to correct the positioning uncertainties after deployment.
The technical problem targeted by the present invention is that of the design of structural elements, the length of which can increase autonomously once the satellite is in station.
There are various deployable structural concepts already in existence: articulated rigid structures (pantographic systems for example), systems relying on the principle of tensegrities (structural assembly in a stable self-constrained state, consisting of a discontinuous set of bars all working in compression mode, linked to a continuous set of cables all working in tension mode), foldable composite bars, flexible membrane type structures, inflatable polymerisable bars, alloys with shape memory, but also bars of measuring tape type.
The applicant has already studied and proven the potential of a telescope structure founded on a hexapod, the legs of which are made up of bars of measuring tape type.
However, it has been shown, by associated deployment modelling and testing, that the deployment of the measuring tapes is very violent and it is difficult to obtain sufficient reliability to allow for autonomous deployment from the platform.
It is possible then to envisage performing this deployment either by means of motors, or by means of a regulation mechanism (for example, a mechanism used in the deployment of the solar panels relying on the use of inertial, viscous dissipation, fluid shear and other such systems). In all cases, these solutions are relatively complex and potential sources of failures.
More specifically, to produce self-deployable measuring tape structures, it has already been proposed to associate two materials comprising a polymer resin with shape memory with which to fix the tape in its wound configuration then force it to be unwound under the effect of a rise in temperature and a composite material with bistable lay-up. This type of lay-up allows a transition from the wound state to the unwound state and vice versa by having to cross only a very small energy jump. Furthermore, each of the two states being a stable state, the tape can remain wound with no holding force.
Nevertheless, this type of solution uses sophisticated materials that are expensive and unavailable in large quantities.
Resins with shape memory necessitate a first initial state in which the material must be deformed by heating it, then by fixing the imposed deformation.